Solution for ruthenium chemical mechanical planarization

ABSTRACT

A solution for ruthenium chemical mechanical planarization containing a nitric acid and an oxidizer is disclosed. A method of forming ruthenium pattern using a polished ruthenium layer is also disclosed. The disclosed solution improves the polishing speed of ruthenium under low polishing pressure, reduces the dishing of ruthenium and decreases scratches generated in the interlayer insulating film. As a result, the disclosed solution and methods improve the techniques for device isolation and reduction of step coverage.

BACKGROUND OF THE INVENTION

[0001] 1. Technical Field

[0002] A solution for ruthenium chemical mechanical planarization(abbreviated as “CMP”) containing a nitric acid and an oxidizer isdisclosed. In particular, the forming method of a ruthenium patternincluding CMP process using the above solution for ruthenium CMP isdisclosed.

[0003] 2. Description of the Related Art

[0004] Ruthenium is a noble metal which is chemically and mechanicallystable, and is an essential material used in fabricating highperformance semiconductor devices. In addition, ruthenium has beenrecently used as lower electrode in forming metal layer/insulatingfilm/metal layer-type capacitors in DRAM devices.

[0005] However, an appropriate CMP slurry cannot be provided to polishthe ruthenium during a CMP process because ruthenium has relatively lowreactivity. Thus, the slurries intended for other metals such astungsten or aluminum are employed when polishing ruthenium.

[0006] The slurries intended for other metals include chemicals forplanarizing of the various metal layers on a silicon substrate. Ingeneral, the slurry for a metal CMP process with a strong acidity of pH2˜4 contains an oxidizer such as hydrogen peroxide (H₂O₂) or ferricnitrate (Fe(NO₃)₂) and an abrasive such as alumina (Al₂O₃) or manganeseoxide (MnO₂). Further, a small amount of surfactant may be added toimprove CMP slurry properties.

[0007] The polishing speed of ruthenium is very slow, thus the CMPprocess is performed for a long period of time under a high polishingpressure in order to adequately planarize the ruthenium.

[0008] As a result, the ruthenium layer may be separated from theinterlayer insulating film because the ruthenium layer has poor adhesionto the interlayer insulating film. In addition, dishing and erosioneffects are generated on the ruthenium layer adjacent to the interlayerinsulating film.

[0009] Moreover, when ruthenium is polished for a long time under highpolishing pressure, the abrasive in the slurry can scratch theinterlayer insulating film severely, and impurities such as the slurrygrounds are generated and remain behind. Therefore, the property of theresultant device is deteriorated.

SUMMARY OF THE DISCLOSURE

[0010] A solution for ruthenium CMP is disclosed which can improve thepolishing speed of ruthenium under a low polishing pressure and reducedishing of ruthenium layer and scratches of the interlayer insulatingfilm.

[0011] A method for forming a metal pattern including CMP process usingthe above solution is also disclosed.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012]FIG. 1 is a cross-sectional view of the ruthenium-formed metalpattern before ruthenium-CMP process using a disclosed solution.

[0013]FIG. 2 is a front view of the metal pattern after ruthenium-CMPprocess using a disclosed solution.

[0014]FIG. 3 is a cross-sectional view of the ruthenium-eliminated metalpattern after ruthenium-CMP process using a disclosed solution.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

[0015] A CMP solution containing a nitric acid and an oxidizer isdisclosed.

[0016] The CMP solution is used for polishing and planarizing ruthenium.

[0017] The nitric acid preferably has a concentration ranging from about0.01 to about 10 M, preferably about 0.01 to about 5 M and a pH rangingfrom about 1 to about 5, preferably about 1 to about 3. When theconcentration of nitric acid is less than 0.1 M, the performance of theoxidizer, such as ceric ammonium nitrate [(NH₄)₂Ce(NO₃)₆] is diminished.

[0018] One preferred oxidizer which oxidizes the ruthenium is cericammonium nitrate and is included in a concentration ranging from about0.01 to about 10 M preferably about 0.01 to about 5 M in the nitricacid.

[0019] It is preferable that CMP solution comprising nitric acidmaintains its pH ranging from about 1 to about 5, preferably about 1 toabout 3, even when the oxidant is added therein.

[0020] The ruthenium CMP solution changes the physical and chemicalproperties of the surface of ruthenium layer by way of the nitric acidin combination with a suitable oxidizer.

[0021] That is, using the disclosed CMP solution, the bonding strengthand compactness between ruthenium atoms are decreased, erosion anddissolution speed of the surface of ruthenium layer are increased, andpolishing speed under the same pressure is improved, resulting in aruthenium layer that is easily planarized.

[0022] In addition, in comparison with conventional slurry, theruthenium CMP solution includes no abrasive and thus decreases scratchesgenerated in the interlayer insulating film.

[0023] A method for preparing the disclosed ruthenium CMP solution willbe described. First, a 0.01˜10 M of nitric acid is prepared, and thenthe ceric ammonium nitrate is added thereto and is stirred to have aconcentration of ceric ammonium nitrate in the range of 0.01˜10 M.

[0024] Thereafter, the resulting mixture is further stirred for about 30minutes so that it is completely mixed and stabilized.

[0025] A method for forming a ruthenium pattern using the disclosedruthenium CMP solution, comprises:

[0026] (a) forming an interlayer insulating film pattern having acontact hole on a semiconductor substrate;

[0027] (b) forming a ruthenium layer on the interlayer insulating filmpattern; and

[0028] (c) performing a ruthenium CMP process on the overall surface ofthe ruthenium layer using the disclosed solution.

[0029] Step (c) may further comprise touch-polishing process upon theresultant of step (c) using slurry for an interlayer insulating film.

[0030] In the first CMP process, the ruthenium-formed semiconductorsubstrate is contacted to a polishing pad formed on a rotary table of aCMP system under pressure.

[0031] Then, the disclosed ruthenium CMP solution is supplied to aninterface of the polishing pad and the ruthenium layer, and theruthenium layer is polished.

[0032] The CMP process is performed under pressure ranging from about 1to about 3 psi, at a table revolution of a rotary type system rangingfrom about 10 to about 80 rpm, and at a linear table speed ranging fromabout 100 to about 600 fpm, depending upon the polishing speed of theruthenium layer and the polishing property of the interlayer insulatingfilm.

[0033] In the second CMP process, touch polishing of interlayerinsulating film is performed at the time the interlayer insulating filmis exposed, using CMP slurry for interlayer insulating film. The touchpolishing is buffering step to prevent ruthenium layer from dishinggenerated by the difference in polishing selectivity between rutheniumlayer and interlayer insulating film.

[0034] Various type of polishing pads can be used in the above CMPprocess according to the polishing properties of the ruthenium layer.For example, a soft pad can be used to raise uniformity of the polishedlayer and a hard pad can be used to improve planarity. And a stack padlaminated with the above two pads or the combination of the above padscan be also used.

[0035] In addition, a metal adhesion layer, such as titanium (Ti) ortitanium nitride (TiN) can be formed on the top surface of theinterlayer insulating film before forming ruthenium layer so as toimprove adhesiveness of ruthenium (see FIG. 1).

[0036] That is, method for forming a ruthenium pattern may comprise:

[0037] (a) forming an interlayer insulating film pattern having acontact hole on a semiconductor substrate;

[0038] (b) forming a metal adhesion layer on the interlayer insulatingfilm pattern;

[0039] (c) forming a ruthenium layer on the metal adhesion layer;

[0040] (d) performing a ruthenium CMP process on the overall surface ofthe ruthenium layer using the disclosed CMP solution until the metaladhesion layer is exposed;

[0041] (e) performing a CMP process on the resultant surface using ametal slurry until the interlayer insulating film is exposed; and

[0042] (f) performing touch-polishing process upon the resultant surfaceusing slurry for an interlayer insulating film.

[0043] Preferably, the interlayer insulating pattern is an oxidepattern, and the ruthenium pattern is used as the lower electrodepattern.

[0044] In the first CMP process, ruthenium-formed semiconductorsubstrate is contacted with a polishing pad formed on a rotary table ofa CMP system under pressure.

[0045] Then, the disclosed ruthenium CMP solution is supplied to aninterface of the polishing pad and the ruthenium layer, and theruthenium layer is polished.

[0046] The CMP process is performed under pressure ranging from about 1to about 3 psi, at a table revolution number of a rotary type systemranging from about 10 to about 80 rpm, and a linear table movement speedranging from about 100 to about 600 fpm, depending upon the polishingspeed of the ruthenium layer and the polishing property of theinterlayer insulating film.

[0047] In the second CMP process, the metal adhesion layer is polished(see FIG. 2).

[0048] In the third CMP process, touch polishing of interlayerinsulating film is performed at the time the interlayer insulating filmis exposed, using the CMP slurry for an interlayer insulating film (seeFIG. 3). The touch polishing is buffering step to prevent rutheniumlayer from dishing generated by the difference in polishing selectivitybetween metal adhesion layer and interlayer insulating film.

[0049] The above CMP slurry for a metal and an oxide film is used thegeneral slurry.

[0050] As discussed earlier, the disclosed CMP process is performed byusing the disclosed ruthenium CMP solution containing ceric ammoniumnitrate in a nitric acid, which improves the polishing speed ofruthenium under a low polishing pressure and reduces the dishing ofruthenium layer.

[0051] In addition, the disclosed solution decreases scratches generatedin the interlayer insulating film because the solution does not containan abrasive.

[0052] As a result, an improved technique for device isolation andreduction of step coverage is disclosed.

What is claimed is:
 1. A CMP solution comprising a nitric acid and anoxidizer.
 2. The solution according to claim 1, wherein the CMP solutionis used for polishing ruthenium.
 3. The solution according to claim 1,wherein the concentration of nitric acid ranges from about 0.01 M toabout 10 M.
 4. The solution according to claim 3, wherein theconcentration of nitric acid ranges from about 0.01 M to about 5 M. 5.The solution according to claim 1, wherein a pH of the solution rangesfrom about 1 to about
 5. 6. The solution according to claim 5, wherein apH of the solution ranges from about 1 to about
 3. 7. The solutionaccording to claim 1, wherein the oxidizer is ceric ammonium nitrate[(NH₄)₂Ce(NO₃)₆].
 8. The solution according to claim 1, wherein theoxidizer is present in concentration ranging from about 0.01 M to about10 M.
 9. The solution according to claim 8, wherein the oxidizer ispresent in concentration ranging from about 0.01 M to about 5 M.
 10. Amethod for forming a ruthenium pattern comprising: (a) forming aninterlayer insulating film pattern having a contact hole on asemiconductor substrate; (b) forming a ruthenium layer on the interlayerinsulating film pattern; and (c) performing a ruthenium CMP process onan overall surface of the ruthenium layer using the CMP solution ofclaim
 1. 11. The method according to claim 10, further comprises: after(c), performing touch polishing process upon the resultant of step (c)using a slurry for interlayer insulating film.
 12. The method accordingto claim 10, wherein the interlayer insulating film pattern is an oxidepattern.
 13. The method according to claim 10, wherein the rutheniumpatterns are used as the lower electrode pattern.
 14. A method forforming a ruthenium pattern comprising: (a) forming an interlayerinsulating film pattern having a contact hole on a semiconductorsubstrate; (b) forming a metal adhesion layer on the interlayerinsulating film pattern; (c) forming a ruthenium layer on the metaladhesion layer; (d) performing a ruthenium CMP process on a overallsurface of the ruthenium layer using the CMP solution of claim 1 untilthe metal adhesion layer is exposed; (e) performing a CMP process on theresultant surface using a metal slurry until the interlayer insulatingfilm is exposed; and (f) performing touch-polishing process upon theresultant surface using slurry for an interlayer insulating film. 15.The method according to claim 14, wherein the interlayer insulating filmpattern is an oxide pattern.
 16. The method according to claim 14,wherein the ruthenium patterns are used as the lower electrode pattern.